How to use Math random method
Description
The Math.random() method returns a random
number between the 0 and the 1, not including either 0 or 1.
Math.random() output within a certain integer
range by using the following formula:
number = Math.floor(Math.random() * total_number_of_choices + first_possible_value)Example
To select a number between 1 and 10:
var num = Math.floor(Math.random() * 10 + 1);
console.log(num);
The code above generates the following result.
Random in a range
To select a number between 2 and 10:
var num = Math.floor(Math.random() * 9 + 2);
console.log(num);
The code above generates the following result.
Random value from an array
To select a random item from an array:
function selectFrom(lowerValue, upperValue) {
var choices = upperValue - lowerValue + 1;
return Math.floor(Math.random() * choices + lowerValue);
} /* w w w . j a va2 s . c o m*/
var colors = ["A", "B", "C", "D", "E", "F", "G"];
var color = colors[selectFrom(0, colors.length-1)];
console.log(color);
The code above generates the following result.
Example 2
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript">
var rand_url = new Array()
rand_url[0] = "http://www.java2s.com";
rand_url[1] = "http://www.java2s.com";
rand_url[2] = "http://www.java2s.com";
rand_url[3] = "http://www.java2s.com";
rand_url[4] = "http://www.java2s.com";
<!--from ww w .ja va 2 s . c o m-->
var rand_num = Math.floor(Math.random() * 5);
document.write("<A HREF='"+rand_url[rand_num]+"'>" + rand_url[rand_num]
+ "</A>");
</script>
</head>
<body>
</body>
</html>